Lens units featured in addition to a primary phoning function in recent camera-mounted mobile phones or the like have a structure in which lenses 2a, 2b, and 2c are integrated with lens barrel 1 to be attached to the main body of the device as shown in FIG. 6.
In FIG. 6, through-hole 3 is created in lens barrel 1. Lenses 2a, 2b, and 2c are press-fitted in this sequence into through-hole 3. Lenses 2a, 2b, and 2c are caught at each step 4 provided inside through-hole 3 to set the distance between lens.
In a conventional lens unit as described above, the number of steps is determined in accordance with the number of lenses configuring the lens unit. The diameter of through-hole 3 between adjacent steps 4 is uniform.
A related prior art is, for example, disclosed in Japanese Patent Unexamined Publication No. 2004-147032.
In FIG. 6, when the diameter of through-hole 3 between steps 4 is uniform, enlargement stress 5, generated while the second lens (e.g., lens 2b) is press-fitted, acts to further broaden through-hole 3 in addition to the stress generated by the lens (e.g., lens 2a) press-fitted first. As a result, this stress 5 concentrates on step 4a holding lens 2a press-fitted first, and may damage lens barrel 1. Accordingly, this operation needs to be conducted in an extremely cautious manner in the manufacturing steps of the conventional lens unit.